PLATINUM-GROUP ELEMENT OXIDES FROM THE PIROGUES OPHIOLITIC MINERALIZATION, NEW-CALEDONIA - ORIGIN AND SIGNIFICANCE

A number of platinum-group element (PGE) oxides and hydroxides have been discovered in a PGE mineralization in the New Caledonia ophiolite complex. They include Pt-Fe oxides containing variable amounts of oxygen (5-50 at. %), Ir-Fe-Rh oxides (metal/oxygen = approximately 3), Fe-Rh-Pt oxides and Pt-Ir-Fe-Rh oxides (metal/oxygen = 1), and an Ru-Mn-Fe phase with a very low metal/oxygen ratio interpreted as hydroxide. These minerals have been found either as inclusions in chromite crystals from chromitite or as discrete grains from alluvial concentrates. Pt-Fe oxides are characterized by unusual textures, including zoning and symplectite. Optical and scanning electron microscope descriptions of all the PGE oxides are given, together with electron microprobe analyses (including the quantitative determination of oxygen). The PGE oxides may result from the alteration of magmatic PGM alloys and from primary crystallization of oxides in lateritic conditions. Their presence indicates the existence of mechanisms of transport and crystallization of PGE (as oxide) in surface conditions, mechanisms contributing to the redistribution and enrichment of PGE in laterite.